Various naturally occurring polypeptides reportedly induce the proliferation of endothelial cells. Among those polypeptides are the basic and acidic fibroblast growth factors (FGF) (Burgess and Maciag, Annual Rev. Biochem., 58: 575 (1989)), platelet-derived endothelial cell growth factor (PD-ECGF) (Ishikawa et al., Nature, 338: 557 (1989)), and vascular endothelial growth factor (VEGF). Leung et al., Science, 246: 1306 (1989); Ferrara and Henzel, Biochem. Biophys. Res. Commun., 161: 851 (1989); Tischer et al., Biochem. Biophys. Res. Commun., 165: 1198 (1989); EP 471,754B granted Jul. 31, 1996.
The heparin-binding endothelial cell-growth factor, VEGF, was identified and purified from media conditioned by bovine pituitary follicular or folliculo-stellate cells several years ago. See Ferrara et al., Biophys. Res. Comm., 161: 851 (1989). Media conditioned by cells transfected with the human VEGF (hVEGF) cDNA promoted the proliferation of capillary endothelial cells, whereas control cells did not. Leung et al., Science, 246: 1306 (1989). VEGF is a naturally occurring compound that is produced in follicular or folliculo-stellate cells (FC), a morphologically well-characterized population of granular cells. The FC are stellate cells that send cytoplasmic processes between secretory cells.
VEGF is expressed in a variety of tissues as multiple homodimeric isoforms (121, 165, 189 and 206 amino acids per monomer), also collectively referred to as hVEGF-related proteins, resulting from alternative RNA splicing. The 121-amino acid protein differs from hVEGF by virtue of the deletion of the 44 amino acids between residues 116 and 159 in hVEGF. The 189-amino acid protein differs from hVEGF by virtue of the insertion of 24 amino acids at residue 116 in hVEGF, and apparently is identical to human vascular permeability factor (hVPF). The 206-amino acid protein differs from hVEGF by virtue of an insertion of 41 amino acids at residue 116 in hVEGF. Houck et al., Mol. Endocrin., 5: 1806 (1991); Ferrara et al., J. Cell. Biochem., 47: 211 (1991); Ferrara et al., Endocrine Reviews, 13: 18 (1992); Keck et al., Science 246: 1309 (1989); Connolly et al., J. Biol. Chem., 264: 20017 (1989); EP 370,989 published May 30, 1990. VEGF121 is a soluble mitogen that does not bind heparin; the longer forms of VEGF bind heparin with progressively higher affinity. The heparin-binding forms of VEGF can be cleaved in the carboxy terminus by plasmin to release (a) diffusible form(s) of VEGF. The amino acid sequence of the carboxy-terminal peptide identified after plasmin cleavage is Arg110-Ala111. Amino terminal “core” protein, VEGF (1-110), isolated as a homodimer, binds neutralizing monoclonal antibodies (4.6.1 and 2E3) and soluble forms of FMS-like tyrosine kinase (FLT-1), kinase domain region (KDR) and fetal liver kinase (FLK) receptors with similar affinity compared to the intact VEGF165 homodimer.
As noted, VEGF contains two domains that are responsible respectively for binding to the KDR and FLT-1 receptors. These receptors exist only on endothelial (vascular) cells. As cells become depleted in oxygen, because of trauma and the like, VEGF production increases in such cells which then bind to the respective receptors in order to signal ultimate biological effect. The signal then increases vascular permeability and the cells divide and expand to form new vascular pathways—vasculogenesis and angiogenesis.
Thus, VEGF is useful for treating conditions in which a selected action on the vascular endothelial cells, in the absence of excessive tissue growth, is important, for example, diabetic ulcers and vascular injuries resulting from trauma such as subcutaneous wounds. Being a vascular (artery and venus) endothelial cell growth factor, VEGF restores cells that are damaged, a process referred to as vasculogenesis, and stimulates the formulation of new vessels, a process referred to as angiogenesis.
VEGF would also find use in the restoration of vasculature after a myocardial infarct, as well as other uses that can be deduced. In this regard, inhibitors of VEGF are sometimes desirable, particularly to mitigate processes such as angiogenesis and vasculogenesis in cancerous cells.
It is now well established that angiogenesis, which involves the formation of new blood vessels from preexisting endothelium, is implicated in the pathogenesis of a variety of disorders. These include solid tumors and metastasis, atherosclerosis, retrolental fibroplasia, hemangiomas, chronic inflammation, intraocular neovascular syndromes such as proliferative retinopathies, e.g., diabetic retinopathy, age-related macular degeneration (AMD), neovascular glaucoma, immune rejection of transplanted corneal tissue and other tissues, rheumatoid arthritis, and psoriasis. Folkman et al., J. Biol. Chem., 267: 10931-10934 (1992); Klagsbrun et al., Annu. Rev. Physiol., 53: 217-239 (1991); and Garner A, “Vascular diseases”, In: Pathobiology of Ocular Disease. A Dynamic Approach, Garner A, Klintworth G K, Eds., 2nd Edition (Marcel Dekker, NY, 1994), pp 1625-1710.
In the case of tumor growth, angiogenesis appears to be crucial for the transition from hyperplasia to neoplasia, and for providing nourishment to the growing solid tumor. Folkman et al., Nature, 339: 58 (1989). The neovascularization allows the tumor cells to acquire a growth advantage and proliferative autonomy compared to the normal cells. Accordingly, a correlation has been observed between density of microvessels in tumor sections and patient survival in breast cancer as well as in several other tumors. Weidner et al., N Engl J Med, 324: 1-6 (1991); Horak et al., Lancet, 340: 1120-1124 (1992); Macchiarini et al., Lancet, 340: 145-146 (1992).
The search for positive regulators of angiogenesis has yielded many candidates, including aFGF, bFGF, TGF-α, TGF-β, HGF, TNF-α, angiogenin, IL-8, etc. Folkman et al., J.B.C., supra, and Klagsbrun et al., supra. The negative regulators so far identified include thrombospondin (Good et al., Proc. Natl. Acad. Sci. USA., 87: 6624-6628 (1990)), the 16-kilodalton N-terminal fragment of prolactin (Clapp et al., Endocrinology, 133: 1292-1299 (1993)), angiostatin (O'Reilly et al. Cell, 79: 315-328 (1994)), and endostatin. O'Reilly et al, Cell, 88: 277-285 (1996). Work done over the last several years has established the key role of VEGF, not only in stimulating vascular endothelial cell proliferation, but also in inducing vascular permeability and angiogenesis. Ferrara et al., Endocr. Rev., 18: 4-25 (1997). The finding that the loss of even a single VEGF allele results in embryonic lethality points to an irreplaceable role played by this factor in the development and differentiation of the vascular system. Furthermore, VEGF has been shown to be a key mediator of neovascularization associated with tumors and intraocular disorders. Ferrara et al., Endocr. Rev., supra. The VEGF mRNA is overexpressed by the majority of human tumors examined. Berkman et al., J Clin Invest, 91: 153-159 (1993); Brown et al., Human Pathol., 26: 86-91 (1995); Brown et al., Cancer Res., 53: 4727-4735 (1993); Mattern et al., Brit. J. Cancer, 73: 931-934 (1996); Dvorak et al., Am J. Pathol., 146: 1029-1039 (1995).
Also, the concentration levels of VEGF in eye fluids are highly correlated to the presence of active proliferation of blood vessels in patients with diabetic and other ischemia-related retinopathies. Aiello et al., N. Engl. J. Med., 331: 1480-1487 (1994). Furthermore, recent studies have demonstrated the localization of VEGF in choroidal neovascular membranes in patients affected by AMD. Lopez et al., Invest. Ophthalmol. Vis. Sci., 37: 855-868 (1996). Anti-VEGF neutralizing antibodies suppress the growth of a variety of human tumor cell lines in nude mice (Kim et al., Nature, 362: 841-844 (1993); Warren et al., J. Clin. Invest., 95: 1789-1797 (1995); Borgstrom et al., Cancer Res., 56: 4032-4039 (1996); Melnyk et al., Cancer Res., 56: 921-924 (1996)) and also inhibit intraocular angiogenesis in models of ischemic retinal disorders. Adamis et al., Arch. Ophthalmol., 114: 66-71 (1996). Therefore, anti-VEGF monoclonal antibodies or other inhibitors of VEGF action are promising candidates for the treatment of solid tumors and various intraocular neovascular disorders. Such antibodies are described, for example, in EP 817,648 published Jan. 14, 1998 and in PCT/US 98/06724 filed Apr. 3, 1998.
Regarding the bone morphogenetic protein family, members of this family have been reported as being involved in the differentiation of cartilage and the promotion of vascularization and osteoinduction in preformed hydroxyapatite. Zou, et al., Genes Dev. (U.S.), 11(17):2191 (1997); Levine, et al., Ann. Plast. Surg., 39(2):158 (1997). A number of related bone morphogenetic proteins have been identified, all members of the bone morphogenetic protein (BMP) family. Bone morphogenetic native and mutant proteins, nucleic acids encoding them, related compounds including receptors, host cells, and uses are further described in at least: U.S. Pat. Nos. 5,670,338; 5,454,419; 5,661,007; 5,637,480; 5,631,142; 5,166,058; 5,620,867; 5,543,394; 4,877,864; 5,013,649; 5,106,748; and 5,399,677. Of particular interest are proteins having homology with bone morphogenetic protein 1, a procollagen C-proteinase that plays key roles in regulating matrix deposition.
In view of the role of vascular endothelial cell growth and angiogenesis in many diseases and disorders, it is desirable to have a means of reducing or inhibiting one or more of the biological effects causing these processes. It is also desirable to have a means of assaying for the presence of pathogenic polypeptides in normal and diseased conditions, and especially cancer. Further, in a specific aspect, as there is no generally applicable therapy for the treatment of cardiac hypertrophy, the identification of factors that can prevent or reduce cardiac myocyte hypertrophy is of primary importance in the development of new therapeutic strategies to inhibit pathophysiological cardiac growth. While there are several treatment modalities for various cardiovascular and oncologic disorders, there is still a need for additional therapeutic approaches.
The present invention is predicated upon research intended to identify novel polypeptides which are related to VEGF and the BMP family, and in particular, polypeptides which have a role in the survival, proliferation, and/or differentiation of cells. While the novel polypeptides are not expected to have biological activity identical to the known polypeptides to which they have homology, the known polypeptide biological activities can be used to determine the relative biological activities of the novel polypeptides. In particular, the novel polypeptides described herein can be used in assays which are intended to determine the ability of a polypeptide to induce survival, proliferation, or differentiation of cells. In turn, the results of these assays can be used accordingly, for diagnostic and therapeutic purposes. The results of such research are the subject of the present invention.